As Neil Tyson has pointed out it seems very unlikely that aliens who figured out inter planetary travel also struggled with landings.

Inter-planetary is easy compared to launch & landing...

Anyway, you send your advance probe, it lands somewhere on the ice sheet and collects a core-samplethat tells you there's a mile of solid rock under the ice... So you send your big-ass space ship, land onthe same sheet of ice, and boy are you surprised to find out it's only 20 or 30 feet of ice with WATER underneath at this spot...